1. Field of the Invention
The present invention is related generally to linearizing apparatuses and methods, and more specifically, to apparatuses and methods which provide a linear relationship between an input signal, such as an input voltage, and a selected or predetermined circuit parameter, such as a frequency response or capacitance.
2. Background Art
The following references are noted herein:                [1] G. M. Rebeiz and J. B. Muldavin, “RF MEMS Switches and Switch Circuits,” IEEE MICROWAVE MAGAZINE, vol. 2, issue 4, pp. 59–71, December 2001.        [2] C. T.-C. Nguyen, “High-Q Micromechanical Oscillators and Filters for Communications (invited),” IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, Hong Kong, Jun. 9–12, 1997, pp. 2825–2828.        [3] D. Young and B. Boser, “A Micromachined-Based RF Low-Noise Voltage-Controlled Oscillator,” IEEE CUSTOM INTEGRATED CIRCUITS CONFERENCE, pp. 431–434, 1997.        [4] D. Young et al., “Monolithic High-Performance Three-Dimensional Coil Inductors for Wireless Communication Applications,” INTERNATIONAL ELECTRON DEVICES MEETING, pp. 3.5.1–3.5.4, 1997.        [5] J. Zou et al., “Development of a Wide Tuning Range MEMS Tunable Capacitor for Wireless Communication Systems,” INTERNATIONAL ELECTRON DEVICES MEETING, pp. 403–406, 2000.        [6] H. Ainspan and J.-O. Plouchart, “A Comparison of MOS Varactors in Fully-Integrated CMOS LC VCO's at 5 and 7 GHz,” EUROPEAN SOLID-STATE CIRCUITS CONFERENCE, 2000.        [7] E. Vittoz and J. Fellrath, “CMOS Analog Integrated Circuits Based on Weak Inversion Operation,” IEEE JOURNAL OF SOLID-STATE CIRCUITS, vol. SC-12, no. 3, pp. 224–231, June 1977.        [8] I. M. Filanovsky and H. P. Baltes, “Simple CMOS Analog Square-Rooting and Squaring Circuits,” IEEE TRANS. ON CIRCUITS AND SYSTEMS I: FUNDAMENTAL THEORY AND APPLICATIONS, vol. 39, no. 4, April 1992.        [9] R. Gregorian and G. C. Temes, “Analog MOS Integrated Circuits for Signal Processing,” New York: John Wiley & Sons, 1986.        
Microelectromechanical systems (“MEMS”) technology has been demonstrated successfully in a variety of RF applications including switching [1], filtering [2], and frequency synthesis [2]. Components such as MEMS varactors [3] and inductors [4], when coupled, have been shown to provide a high quality factor (Q-factor) reference for voltage controlled oscillators (“VCOs”) [3] when compared to alternative integrated technology. Several parallel plate varactor topologies have been reported with impressive results [3][5]. However, a significant drawback associated with the parallel plate topology is the highly nonlinear tuning or frequency response as a function of the electrostatic actuation of the device.
Other devices also exhibit nonlinear characteristics, such that a selected or predetermined device parameter has a nonlinear relationship to an input or control signal, such as an input voltage. In addition to MEMS varactors, the frequency response of parallel plate capacitors, more generally, has a nonlinear relationship to the voltage of the capacitor. Similarly, junction varactors and metal oxide semiconductor (“MOS”) varactors also exhibit such nonlinear characteristics.
Tuning of such capacitors to a selected or predetermined frequency, as part of an oscillator, for example, as a nonlinear response, is comparatively difficult. In the prior art, the nonlinear frequency response is modeled, with particular voltage levels (as coefficients) specified for corresponding frequencies. The resulting modeled coefficients are stored as a look-up table in memory, which is subsequently accessed to tune a particular device to a selected frequency. Such an implementation, however, requires additional processing circuitry, a memory circuit, and memory interface circuitry. In addition, to the extent fabrication varies from assumed modeling parameters, such stored coefficients are inaccurate, and do not provide the desired result of tuning such a device to a selected frequency.
As a consequence, a need remains for a more robust and accurate solution for selecting or determining device parameters, such as for tuning a device to a particular frequency, when such parameters have a nonlinear relationship to corresponding input or control signals. Such a solution should be capable of being implemented using existing integrated circuit fabrication technology, without the additional need for memory and memory interface circuitry.